(1) FIELD OF THE INVENTION
The present invention relates to a water jet type air compressor system into which water is jetted in order to perform lubrication or the like, a starting method for the system, and a water quality control method for the system.
(2) DESCRIPTION OF THE RELATED ART
FIG. 1 is a schematic view of a screw compressor. In this drawing, a screw compressor 10 is a biaxial screw compressor, which is constituted of two screw rotors 1, bearings 2a, 2b, a high pressure seal (e.g., a mechanical seal 3), a low pressure seal (e.g., a lip seal 4), a compressor main body 5 and the like. This screw compressor 10 rotatively drives two screw rotors 1 engaged with each other, compresses the air introduced from an air intake 5a between the two rotors, and discharges the compressed air from a discharge opening 5b. Incidentally, the mechanical seal can also be used as the low pressure seal, and in this case, water is supplied to both mechanical seals.
FIG. 2 is an external view of the screw compressor of FIG. 1. In this drawing, 6a is a pulley for driving the rotors and 5c is a water supply port to the mechanical seal. In the compressor of such screw compressor, since seal faces or frictional faces (the material of which is carbon or ceramics) of the rotors 1 and the mechanical seal 3 have a structure of directly sliding, water is jetted and supplied from the air intake and the water supply port 5c so as to lubricate the sliding faces. Incidentally, this water serves not only to lubricate and cool the sliding faces, but also to improve compression efficiency by cooling the compressed air.
FIG. 3 is a block diagram of the air compressor equipment using such a water jet type compressor. In this drawing, 7 is a fan motor (a motor with fan), 8 is a water tank, and 9 is a water cooler. The fan motor 7 drives the pulley 6b with a fan 7a for blowing the air to the water cooler 9, and rotatively drives the pulley 6a for driving the rotors by a belt. By the rotative driving of the pulley 6a, the inner rotors rotate, and the air is introduced from an air introducing line 12a through the air intake 5a. A compressed air compressed between the rotors is supplied to the water tank 8 from the discharge opening 5b through a compressed air line 12b.
In the water tank, water is supplied up to an intermediate position, and the inner water is forcibly fed to the water cooler 9 through a water line 13a by pressure (about 0.7 Mpa: about 7 Kg/cm.sup.2 g) of pressurized air supplied to the upper part, and here it is cooled and, further, it is supplied to the air intake and the water supply port 5c of the compressor 10 through a water line 13b and jetted inside thereof. The water which has lubricated and cooled the inside of the compressor 10 is circulated in the water tank 8 with the pressurized air, separated by a mist separator 8a, and mixed with the inner water inside the water tank 8. On the other hand, the pressurized air from which water content is eliminated is ejected from a check valve 8b.
As described above, in the conventional water jet type air compressor system, water is supplied to the rotors or the mechanical seal of the water jet type compressor 10 during operation, thereby providing for lubrication and cooling. However, when the compressor stops and pressure inside the water tank 8 continues to be in a normal pressure state for a long time, since the compressor is usually located at a high position, the water level goes down and the water line 13a and the inside(the rotors and the mechanical seal) of the compressor 10 are kept in a dry state.
For this reason, when the compressor was started in this dry state (hereinafter referred to as a dry operation), there was a problem in that the compressor was operated in a dry state during the time till a circulating water arrived at the rotors and the mechanical seal. This dry operation time is the time until pressure inside the water tank is increased by driving the compressor and the circulating water arrives at the rotors or the mechanical seal by pressure of the compressed air. This dry operation time is, for example, about 5 to 10 seconds. During this dry operation, there has been a problem in that lubricating and cooling effect are not available owing to the dry state, and compared to a state wherein water is supplied, wear and temperature rise of the rotors or the mechanical seal become severe, thereby causing inconveniences such as damages or lowering of the performance and shortening of the exchange cycle.
On the other hand, as described above, in the conventional water jet type air compressor system, water is supplied to the rotors or the mechanical seal of the water jet type compressor 10 during operation, thereby providing for lubrication and cooling. This water is circulated between the water tank and the compressor, and a part of the water mist contained in the compressed air and an evaporated water content (a vapor) are not separated by the mist separator 8a but supplied to a supply destination from an air outlet. Hence, there has been a problem in that the circulating water was gradually reduced, thereby requiring a periodic replenishment of the water.
Further, since no impurity is contained in the vapor lost by evaporation, when ordinary service water containing a hard component is used as starting water, there has been a problem in that impurities in the circulating water condensed and scale trouble occurred. For this reason, a demineralizer or a water quality purifying device becomes indispensable, which makes the system complex and expensive. Further, the cyclic exchange of ion exchange resin or filters becomes indispensable for the demineralizer or the water quality purifying device, thereby incurring a maintenance cost.
Further, there is a problem in that impurities in the circulating water, particularly solid material have a bad effect on frictional faces of the mechanical seal or the rotors and increases wear thereof. In order to eliminate such solid material, a filter is disposed in the circulating water path. However, if filtering accuracy is enhanced, not only is the exchange cycle of the filter shortened, but also elimination of microscopic particles by the filter as such is difficult.
Further, when the circulating water is continuously used for a long time, bacteria is bred in the circulating water, and this bacteria, accompanied by the compressed air with water mist, becomes a source of asthma and allergies. Hence, in the conventional water jet type air compressor system, there has been a problem in that the inner circulating water was required to be exchanged by periodically stopping the system with a result that a working rate of the system was reduced.
To solve these problems, for example, Japanese Patent Application Laid-open No. 1448387/1983 discloses an "Adjustment method of the water for compressor". However, this method simply and automatically supplies the water by disposing a sensor, and does not basically solve the problems as described above.